This invention relates to apparatus, in the form of a unitary instrument, for measuring and indicating a plurality of electrical values and functions of a three-phase alternating current power system, and also single-phase and DC systems.
An object of this invention is to provide novel apparatus for a three-phase power system for measuring and indicating amperage, resistance, line voltage, phase voltage, ground detection, and phase sequence.
Another object of this invention is to provide novel apparatus which performs more of such functions with less components, in relation to known apparatus of this type.
A further object of this invention is to provide apparatus of this type wherein measurements of line voltage, and and phase voltage, and phase sequence detection and ground detection share the same components.
A still further object of this invention is to provide a novel apparatus for measuring and indicating electrical functions, including phase voltage, on any grounded or ungrounded three-phase system, without connection to a neutral or ground of that system.
Still another object of this invention is to provide novel apparatus including means to indicate phase sequence without the aid of lamps or other special equipment.
These objects are accomplished in apparatus which includes a meter movement for indicating the flow of current and the following associated apparatus circuitry, First, second and third phase-conductors serve to connect the three phases of the external circuit to the apparatus circuit. First, second and third phase-resistors, of equal value, are connected to a common juncture, with a first of said phase-resistors being in series with the meter movement. A selector switch connects the three phase-conductors to the three phase-resistors, and selects three alternative connective relationships between the phase-conductors and the phase-resistors. A switch in series with the third phase-resistor and the common juncture selectively opens and closes this circuit. A phase-component having a different impedance than the phase-resistors is connected with the third phase-resistor to a common terminal of the three position selector switch; and a switch in series with the phase-component and the common juncture selectively opens and closes this circuit.